This means revolutions per minute. This is not how many times your tires are turning per minute, but its how many cycles the engine is going through each minute. i.e revs per minute.
1 rev = 1 push-bang-blow-suck.
when you step on the accelerator pedal, you add petrol to the engine, the petrol mixes with the air and burns and causing the engine to spin more. The further you "rev" the faster the engine spins. I.e....the higher the RPM.
You'll notice some cars have a huge RPM meter (its called Tachometer if you didnt know) especially in sports cars. This is because to a car enthusiast, the rpm meter is much more important than the speed meter. An average car user doesnt care about all this because car is to get from A to B only.
Monitoring your revs is important because it lets you judge and decide how to use your petrol wisely and also it lets you command the car if you want to drive fast for some particular reason.
You'll see a red line, this is called the er....red line region.
Normally in racing mode, you change gears just after the red line.
But for normal everyday driving, you change gears at where your torque peaks. I'll get back to that later.
For even lazier grandma driving (depends on who's grandma) you shift gears at around 3000 rpm.
Speed meter (or Speedometer)
kinda self explanatory. The speedometer gives you the current speed of your gearbox and hence, gear.
So if you are travelling 100 kmph, the particular gear you are in is "travelling" 100 kmph.
Not so important for racers, because speed isnt important. The most important thing in a race is to be infront of the pack, Michael Schumacher was good at this. And so is Valentino Rossi. Speed is just a number.